Splash screen is optional. Also remove some unused class definition.

- allow unit tests to use QGCApplication
- clear global singletons for each unit test run

Subclass of QMessageBox which re-implements the static public
functions. There are two reasons for this:
1) The QMessageBox implementation on OSX does now show the title
string. This leads to message boxes which don't make much sense. So on
OSX we set title to text and text to informative text.
2) If parent is NULL, we set parent to MainWindow::instance. This
prevents message boxes which can go behind MainWindow

Do not dynamic cast or de-reference QObject, since object is either in
destructor or may have already been destroyed.

Plus change to use QGCFileDialog

Using QFileDialog directly on OS X can hang intermittently due to Qt
bug.

- Logging now always on to temp file
- User prompted to save temp file after disconnect
- Orphaned temp logs checked for on boot
- Logs saved to new save file location
- Log file starts/stops with first and last connnection

Also renamed from QGCSettingsWidget to SettingsDialog to better reflect
usage.

This avoids collision with main app SettingsDialog class

Map widget: make all connections that might suffer from multiple connect logic issues unique, found by Nyaruko

This way OS X correctly positioned menu items

This allows you to filter the list of parameters the widget displays.

This allows you to determine if full parameter list is ready if you
missed the parameterListUpToDate signal.

Also fixed bug in loadStyle